A cable or conduit is sometimes installed underground leaving the environment where the cable or conduit is placed with an aesthetically pleasing appearance. The cable or conduit can be placed into a trench dug into the ground. Alternatively, underground drilling allows for the placement of cable or conduit underground without having to dig a trench the length of the cable or conduit. Such a procedure can be used to install cable or conduit under difficult to trench areas such as roads, rivers, or wetlands. Directional drilling allows for guided drilling of the hole to bypass obstructions or other areas undesirable to drill through.
To place the cable or conduit underground in a drilling operation, a hole is typically drilled underground from an above ground starting point to an above ground end point with equipment including a drill bit rotated through the ground by a drilling rig located above ground at the starting point. Once the hole is drilled from the starting point to the end point, the cable or conduit can be pulled back through the hole from the end point to the starting point. The pulling operation may be accompanied by a procedure whereby the hole initially drilled through the ground is enlarged or widened with a reamer and/or packer during the pulling operation. The widening operation typically utilizes rotational torque from the drilling rig located at the starting point. In that case, the drilling rig rotates a reamer or other widening tool to widen the hole. It is desired to attach the cable or conduit to the underground widening equipment so that the cable or conduit is pulled through the hole as the hole is widened by the widening equipment.
Rotations of about 150 to 200 revolutions per minute or more by the drilling rig may be utilized during the widening operation. It is desirable to prevent the transfer of rotational torque from the rotating widening equipment to the cable or conduit during pulling of the cable or conduit. A swivel can be utilized to prevent the transfer of rotational torque from the widening equipment to the cable or conduit. One concern in this area is that the swivel be able to withstand the tension loads encountered during pulling of the cable or conduit by the widening equipment without transfer of the rotational torque to the cable or conduit.
Another concern in the area of cable or conduit pulling is the presence of liquids and/or solids which pose a contamination risk with respect to any moving parts of the swivel. The hole may include naturally occurring water, mud, dirt, sand or rocks. The drilling and/or widening operation may also be accompanied by the use of flowing liquid added to assist in the formation of the hole and/or to remove particles from the hole. Bentonite may be added to the liquid to assist in removal of the dirt and rock particles. Bentonite is a very fine particle that is difficult to seal from contact with moving parts.
In addition to the desire to prevent the transfer of rotational torque during tension loadings, other concerns arise for pulling cable or conduit during the widening operation. In the case of underground drilling, the drilling operation to form the hole may be accomplished via directional drilling techniques where the drill bit is steered and/or moved about in a non-linear path during drilling from the starting point to the end point. Such non-linear drilling path can cause side load problems during the widening operation as the widening equipment and swivel traverse the curves.
Also, during the widening and pulling operation, an obstruction in the hole may be encountered where it is desirable to push back on the widening equipment in a direction from the starting point toward the end point. The pushing operation puts a compression loading on the swivel. The side load problem and the pushing problem create concerns for any swivel apparatus provided between the widening equipment and the cable or conduit.
In addition, other concerns arise during the widening and pulling operation including the desirability of a relatively high tension load to be placed on the swivel to accomplish the pulling operation, and the desirability of a relatively small diameter and length to the swivel.
There is a need in the art for a swivel apparatus which address the above concerns and other concerns.